Update From The State Veterinarian: EHV-1

Horses at a boarding facility in central North Carolina have been confirmed to have the neurologic form of EHV-1. This facility has had little movement of horses on or off the farm. Our veterinarians are working closely with the practicing veterinarian and the farm owner. The premises has been quarantined and strict biosecurity measures have been in place since Dec. 23. All animals are having temperatures monitored twice a day, and no horses have had fevers or other clinical signs since Friday, Dec. 27, 2013, the first day there were confirmed lab results from the National Veterinary Services Laboratory. The quarantine will be held for 28 days after the last fever is recorded.

Additional investigation found that five horses were moved from the stable in the last four weeks and have been tracked to four locations in North Carolina where their health status is being monitored. All known exposed horses have been accounted for, are not showing clinical signs and have not been moved. No additional horses have been moved from any of the known sites.

At this point, we believe this is an isolated incident with low-risk to other horses. However, we do encourage horse owners to practice good biosecurity measures as a precaution. EHV-1 is not a reportable disease to the Office of the State Veterinarian under state law, however the office appreciates being made aware of suspicious cases and will offer help in controlling the disease. The last known case in North Carolina was in January 2012.

What is EHV-1?

EHV-1 (equine herpesvirus-1) is one of a large group of DNA viruses causing potentially serious disease in horses and other species. EHV-1 has two forms: one that causes abortion in mares and one that causes respiratory infection and neurological symptoms. The above cited outbreaks have involved the EHV-1 respiratory/neurological form of the virus causing a condition known as Equine Herpes Myeloencephalopathy (EHM).EHV-1 is contagious and is spread by direct horse-to-horse contact, by contaminated hands, equipment and tack, and, for a short time, through aerosolization of the virus within the environment of the stall and stable.

What are the Clinical Signs of EHV-1?

The initial clinical signs of the infection may be nonspecific and include fever of 102°F or greater. Fever may be the only abnormality observed. Other presenting signs may be combinations of fever and respiratory symptoms of nasal discharge and cough. Some horses have reddish mucous membranes. Horses with neurological disease caused by EHV-1 infection can soon become uncoordinated and weak and have trouble standing. Difficulty urinating and defecating may also occur. Often the rear limbs are more severely affected than the front. Signs of brain dysfunction may occur as well, including extreme lethargy and a coma-like state. The incubation period of EHV-1 infection is HIGHLY VARIABLE, depending on the host, on the virulence of the virus, and on environmental and other factors such as stress. The AVERAGE incubation period is 4 to 7 days, with the majority of cases being 3 to 8 days, but with some taking up to 14 days. When neurological disease occurs, it is typically 8 to 12 days after the primary infection involving fever. In most cases, horses exposed to EHV-1 will develop a fever and possibly nasal discharge and then go on to recover.

University of California, Davis, School of Veterinary Medicine

Submitted by Jared Harrell